HiRide is correct about the Dyno Dynamics. We had both a Dynojet AND a Dyno Dyamics at my old shop. Dyno Dynamics Dyno's usually read about 15% less than typical Dynojet Dyno's.
You might ask, why did I have both dyno's? Simple, the Dynojet was only a 2WD dyno...and I had a lot of customers with WRX/EVO/S4/Skyline's...so I ended up purchasing a Dynamics Dyno which can be used for either AWD or 2WD. We just never got rid of the Dynojet so we had a direct comparison between the two.
2008 CLK63 Black
2006 CLS55 AMG
2004 BMW M3
1998 Nissan S14 240sx, powered by RB26
1990 Nissan S13 240sx, 630 whp SR20DET
1995 Subaru Legacy, EJ20R, 410 whp
Soon to have 2011 Ford Mustang 5.0